Comets didn't wipe out early Americans 12,900 years ago

Published: Saturday, October 24, 2009, 12:38 [IST]

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Washington, October 24 (ANI): In a new research, scientists have suggested that a comet impact didn't set off a 1,300-year cold snap that wiped out most life in North America about 12,900 years ago, including sabertooth tigers and early Americans.

Though no one disputes the frigid period, more and more researchers have been unable to confirm a 2007 finding that says a collision triggered the change, known as the Younger Dryas.

The drop in temperature, plus fires from the impact, wiped out sabertooths, mastodons, and other giant animals, and may have caused the decline of an early civilization known as the Clovis culture.

The 2007 research was based on a combination of archaeological artifacts and extraterrestrial magnetic grains in soil samples found in a thin layer of sediment throughout North America.

The original team, led by Richard Firestone, a nuclear chemist at Lawrence Berkeley National Laboratory, also found what he said are traces of charcoal and microscopic bits of carbon from intense fires ignited by the collision.

However, according to a report in National Geographic News, a new research has taken aim at all of these findings.

Nicholas Pinter, a geologist at Southern Illinois University, argued that black mats described as charcoal in the 2007 research weren't actually charcoal.

Instead they were from ancient, dark soil formed in a long-ago wetland, according to Pinter.

"It's a misunderstanding of what these layers represent," he said. Likewise, the small amounts of carbon "are not uniquely associated with high-intensity fire," he added.

As for the magnetic grains, they are likely from the 30,000 tons of tiny meteorites that fall to Earth each year.

Pinter found such grains in equal or greater concentrations at many other layers dating to other time periods.

According to Vance Holliday, an archaeologist at the University of Arizona, there is no sign that the demise of the Clovis culture was caused by a comet crash.

Around the time of the cold snap, the style of spearpoints changed, which Firestone and colleagues argued was evidence that the Clovis peoples had declined due to the comet impact.

But, Holliday said it reflects a normal evolution in preference. He compared spearpoint designs to the appearance-and disappearance-of tail fins on classic automobiles.